The function jul
is used to create jul
(julian date)
objects, which are useful for date calculations.
as.jul
and asJul
coerce an object to class "jul", the
difference being that as.jul
calls the constructor jul
,
while asJul
simply forces the class of its argument to be "jul"
without any checking as to whether or not it makes sense to do so.
is.jul
tests whether an object inherits from class "jul".
jul(x, …)
# S3 method for Date
jul(x, …)
# S3 method for IDate
jul(x, …)
# S3 method for ti
jul(x, offset = 1, …)
# S3 method for yearmon
jul(x, offset = 0, …)
# S3 method for yearqtr
jul(x, offset = 0, …)
# S3 method for default
jul(x, …)
as.jul(x, …)
asJul(x)
is.jul(x)
object to be tested (is.jul
) or converted into a jul
object. As described in the details below, the constructor function
jul
can deal with several different kinds of x
.
other args to be passed to the method called by the generic
function. jul.default
may pass these args to as.Date
.
For jul.ti
, a number in the range [0,1] telling where in the
period represented by x
to find the day. 0 returns the first
day of the period, while the default value 1 returns the last day of
the period. For example, if x
has tif
= "wmonday" so
that x
represents a week ending on Monday, than any
offset
in the range [0, 1/7] will return the Tuesday of that
week, while offset
in the range (1/7, 2/7] will return the
Wednesday of that week, offset
in the range (6/7, 1] will
return the Monday that ends the week, and so on.
jul.yearmon
and jul.yearqtr
work on yearmon
and
yearqtr
objects from zoo. Note that the default
offset
for these functions is 0, not 1, as that is how the
other index-to-date functions in zoo work, i.e, if ym
is a yearmon
object, then as.Date(ym)
and
as.jul(ym)
should give the same date.
is.jul
returns TRUE
or FALSE
.
as.jul
and asJul
return objects with class "jul".
jul
constructs a jul
object like x
.
jul
with no arguments returns the jul
for the current day.
The jul
's for any pair of valid dates differ by the number of
days between them. R's Date
class defines a Date as a number
of days elapsed since January 1, 1970, but jul
uses the
encoding from the Numerical Recipes book, which has Jan 1, 1970
= 2440588, and the code for converting between ymd and jul
representations is a straightforward port of the code from that tome.
Adding an integer to, or subtracting an integer from a jul
results in another jul
, and one jul
can be subtracted
from another. Two jul
's can also be compared with the
operators (==, !=, <. >, <=, >=
).
The jul
class implements methods for a number of generic
functions, including "["
, as.Date
, as.POSIXct
,
as.POSIXlt
, c
, format
, max
,
min
, print
, rep
, seq
, ti
,
time
, ymd
.
jul
is a generic function with specialized methods to handle
Date
and ti
objects. A recent addition is a method to
handle IDate
objects as defined in the data.table
package.
The default method (jul.default
) deals with character x
by
calling as.Date
on it. Otherwise, it proceeds as follows:
If x
is numeric, isYmd
is used to see if it could be
yyyymmdd date, then isTime
is called to see if x
could
be a decimal time (a number between 1799 and 2200). If all else fails,
as.Date(x)
is called to attempt to create a Date
object
that can then be used to construct a jul
.
Press, W. H., Teukolsky, S. A., Vetterling, W. T., and Flannery, B. P. (1992). Numerical Recipes: The Art of Scientific Computing (Second Edition). Cambridge University Press.
# NOT RUN {
dec31 <- jul(20041231)
jan30 <- jul("2005-1-30")
jan30 - dec31 ## 30
feb28 <- jan30 + 29
jul() ## current date
# }
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